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(EXP3/09) Suppression of Magnetic Islands Through Synchronous and Asynchronous Application of Resonant Magnetic Fields

M. Mauel, J. Bialek, C. Cates, H. Dahi, D. Maurer, D. Nadle, G. A. Navratil, M. Shilov, and E. Taylor

Department of Applied Physics, Columbia University New York, NY 10027, USA

Abstract.  Observations of the suppression of the amplitude of tearing instabilities through the application of synchronous (closed loop) and asynchronous (open loop) resonant magnetic perturbations are reported. These observations extend our previous investigations of large changes of tearing mode rotation induced by oscillating currents in small saddle coils. Although mode suppression is achieved using several techniques, the most significant decrease in the size of a magnetic island occurs when the island is made to rotate faster or slower than its natural frequency. By comparing measurements with time-dependent simulations, we find the observed mode suppression is consistent with a dynamic stabilizing effect proportional to the square of the difference between the island's instantaneous and time-averaged rate of toroidal rotation. Our results suggest that internal modes may be controlled more effectively by inducing rapid modulations of island rotation than by applying phase-controlled active-feedback.

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IAEA 2001